9
19. Make sure the unit is free of “rattles”, and the tubing in the unit is free from excessive vibration. Also make sure tubes
or lines are not rubbing against each other or sheet metal surfaces or edges. If so, correct the trouble.
20. Set the thermostat at the appropriate setting for cooling and heating or automatic changeover for normal use.
21. Be sure the Owner is instructed on the unit operation, filter, servicing, correct thermostat operation, etc.
The foregoing “Start-up Procedure and Check List” is recommended to serve as an indication that the unit will operate
normally.
COMPONENTS
1. Contactor
- This control is activated (closed) by the room thermostat for both heating and cooling. The contactor has
a 24V coil and supplies power to the compressor and outdoor fan motor.
2. Crankcase Heater –
This item is “ON” whenever power
is supplied to the unit and the crankcase heater thermostat is
closed. Crankcase heater thermostat closes at 67° and opens at 85°. It warms the compressor crankcase thereby
preventing liquid migration and subsequent compressor damage. The insert type heater is self regulating. It is
connected electrically to the contactor L1 and L2 terminals.
3. Condenser Motor -
This item is activated by the contactor during heating and cooling, except during defrost and
emergency heat operation.
4. Compressor -
This item is activated by the contactor for heating and cooling, except during emergency heat. It is
protected by
an internal overload.
5. Contactor Relay -
This control is activated by the thermostat (24V coil) and supplies power to the contactor.
6. Defrost Control
- The Defrost control provides time/temperature initiation and termination of the defrost cycle.
When a Defrost cycle is initiated, the defrost control shifts the reversing valve to “cooling” mode, stops the outdoor
fan and brings on supplemental heat. Normally, a Defrost cycle will take only 2-3 minutes unless system is low on
charge or outdoor conditions are severe. (Windy and cold.) The defrost control also provides for a 3 minute off cycle
compressor delay.
7. Outdoor Thermostat -
These optional controls are used to prevent full electric heater operation at varying outdoor
ambient (0° F-to 45° F). They are normally open above their set points and closed below to permit staging of indoor
supplement heater operation. If the outdoor ambient temperature is below 0° F (-18° C) with 50% or higher RH, an
outdoor thermostat (OT) must be installed and set at (0°) on the dial. Failure to comply with this requirement may
result in damage to the product which may not be covered by the manufacturer’s warranty.
8. Reversing Valve Coil -
This coil is activated by the thermostat, in the cooling mode and during defrost. It positions
the reversing valve pilot valve for cooling operation.
9. Indoor Blower Motor
Units with EEM Motors
The EEM model indoor blower motor is activated by the room thermostat by COOLING/
HEATING or FAN ON position. The motor is energized by a 24 volt control signal (from thermostat Y, G or W) for EEM
motors. EEM motors are constant torque motors with very low power consumption.
(See
Air Flow Measurement and Adjustment
for speed adjustment instructions).
10. Blower Interlock Relay -
This relay is used to energize the blower during the electric heat operation. Some room
thermostats do not energize the motor during electric heat. This relay insures blower operation when the room
thermostat energizes heat. This relay has a 240 volt coil and an 8 amp contact relay. This relay is energized by the
electric heat kit sequencer.
EXPLANATION AND GUIDANCE (HEAT PUMP)
The heat pump is a relatively simple device. It operates exactly as a Summer Air Conditioner unit when it is on the cooling
cycle. Therefore, all the charts and data for service that apply to summer air conditioning apply to the heat pump when it
is on the cooling cycle, and most apply on the heating cycle except that “condenser” becomes “evaporator”, “evaporator”
becomes “condenser”, “cooling” becomes “heating”.
When the heat pump is on the heating cycle, it is necessary to redirect the refrigerant flow through the refrigerant circuit
external to the compressor. This is accomplished with a reversing valve. Thus, the hot discharge vapor from the compressor
is directed to the indoor coil (evaporator on the cooling cycle) where the heat is removed, and the vapor condenses to
liquid. It then goes through the expansion device to the outdoor coil (condenser on the cooling cycle) where the liquid is
evaporated, and the vapor goes to the compressor.
When the solenoid valve coil is operated either from heating to cooling or vice versa, the piston in the reversing valve to
the low pressure (high pressure) reverse positions in the reversing valve.
Figure 7 shows a schematic of a heat pump on the cooling cycle and the heating cycle. In addition to a reversing valve, a
heat pump is equipped with an expansion device and check valve for the indoor coil, and similar equipment for the outdoor
coil. It is also provided with a defrost control system.
The expansion devices are flowrator distributors and perform the same function on the heating cycle as on the cooling
cycle. The flowrator distributors also act as check valves to allow for the reverse of refrigerant flow.
